This is the 'New Look', created by Christian Dior in 1947. It was a very conscious shift away from the restrictions and sumptuary constraints of the war, and a move to a very different way of feeling about how you looked and how you lived. It was a move away from narrow profiles, limited use of cloth, 'make do and mend' and women's clothes designed for working in munitions factories. It used twenty metres of fabric for an outfit instead of two.

This was a big change - many people were furious at the 'waste' of fabric. Indeed, it was so different that some outraged Parisiennes physically attacked a woman wearing the clothes.

Who, really, were they angry with, though? There's a common idea that in some way fashion designers get together in a room and decide what the fashion will be next year. That's a pretty fundamental misunderstanding. Rather, they propose what might fit the zeitgeist. Sometimes that's incremental and sometimes it's a radical break - sometimes the pendulum needs to swing from one extreme to another. Sometimes they get it wrong, but when they get it right it captures an age. The New Look proposed that people wanted to move on from the clothes of wartime austerity, and from austerity itself, and that this was a good way to do it, and Dior was right.

You can see the same dynamic with punk, which unlike the New Look wasn't proposed by designers at all but came from the bottom up, but which served the same purpose - here was a look and an attitude that expressed how people felt, and, again, was a reaction against a very different kind of look that went before. Punk was picked up and perhaps popularised or accelerated by designers (and people argue about how), but the point is the same - no-one sits in a room to decide what the fashion is going to be. Fashions express what people themselves want.

I'm reminded of these kinds of shifts when thinking about Facebook and how much it can change behaviours - about how much it can decide what the new thing will be. After all, social media has now moved far past the point that it serves any kind of purely utilitarian purpose. There was a time when instant messaging or the asymmetric feed were simply better person-to-person mechanics than email (as one could argue that Slack is now). Now, though, we're shifting around at the top of Maslow's hierarchy of needs, experimenting with different ways to explore and express our personality and our needs, and so, in a sense, of the zeitgeist. Many of these trends have also expressed the same sense of a pendulum - we swung from the chaos of MySpace to the structured order of Facebook, and then swung again to the fun and exuberance and creativity of Snap (or at any rate that Snap aspires to have). But Snap of course is not the only one - sitting on top of the smartphone, which is itself a social platform, there are dozens of apps and experiences, from GIF keyboards to live streaming apps to animoji, all trying to capture a little piece of Maslow. Social is pop culture.

This gets to why I think it's wrong to say, deterministically, that Facebook gets to decide what we do on its platform or what we see in the newsfeed. This, to me, is very like saying that a fashion designer gets to decide what we'll wear. They do... a bit. They can decide what colours to put in the shop. They can change the cut. They have marketing and models and glamour and all the tools of influence of the industry. They can optimise an idea to improve use or sales. But fashion collections fail, and fashion retailers fail, and the looks that work reflect what people actually want, not because they knew they wanted that or because you could ask them in any mechanistic way or because you're tracking metrics, but because they're a proposal that turns out to capture how people feel. You can optimise a product, and measure it, but people still have to want it. Facebook can fill the home page with a feature, and a retailer can fill a shop with a look, but that doesn't mean you can make people take it. You can only propose. And the more and faster feedback you have, the more data you get but the less control - the more obvious it is that this idea isn't working, no matter what was in your Powerpoint.

Indeed, when something becomes fashionable, it will inevitably become unfashionable - "no-one goes there anymore - it's too crowded". The zeitgeist changes both of itself and because of your success. So the very fact that any social media company has found a behaviour that people want means that at some point they'll stop wanting it. People stopped wearing the new look, they stopped wearing miniskirts, and they stopped wearing punk. There is always a pendulum. A good designer can feel this before it happens, not after, and so for Facebook: when Facebook says "games have great metrics and make us lots of money, but we think they make the Facebook experience worse so we'll kill them", and, more recently, when Snap says "we think the algorithmic linear feed is bad", this is also a proposal, and, again, it might be wrong. It might be suggested by detailed daily metrics, or a vague instinctive sense of, again, the zeitgeist, but the crucial point is that whether this is right - whether people like it - is never fundamentally determined by the company. This applies at every level of scale - whether it's creating an entirely new product or tuning some small feature based on a daily or hourly feedback loop - Facebook doesn't determine what the feedback tells it.

One can also suggest that though this product or this style found the moment, others were possible too, and that though the company or the designer pursued this one, if they'd pursued others then those others might have happened instead. Sometimes this is true, but one needs to be careful to avoid conflating that with the alternative that you wish had happened. You might not like this fashion or that product, but the alternative equilibrium might have been worse, might not exist, or might have needed quite different people to find. And it might still be coming.

Hence, one of the ways I describe Facebook is that it is extremely good at surfing user behaviour - it tries to work out where users are going and go with them, whereas Snap tries much more to try to get ahead of this. In different ways both of these are also what a great designer does, and, likewise, Bismarck said that the great statesman listens for the footsteps of god walking through history and tries to grab onto his coat as he passes. Of course, for Facebook that sometimes means creating things (and here the surf metaphor breaks a little, as you can't shape the wave), even things that users say they don't like. Dior's New Look made people angry and so did the original newsfeed itself. But then, fashion designers create looks all the times - that doesn't mean they can make anyone wear it. You can shape things, sometimes. You can ride and channel the trend. But I think we attribute vastly too much power to a handful of product managers in Menlo Park, and vastly too little power to the billions of people who look at their phone screen and wonder which app to open. Facebook writes algorithms, and designers cut the cloth, but that doesn't mean they control what people look at or what people wear.

I work at Andreessen Horowitz ('a16z'), a venture capital firm in Silicon Valley that invests in software companies. I try to work out what's going on and what will happen next.

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